Integral 3D humic acid-carbon hybrid foam and devices containing same

ABSTRACT

Provided is an integral 3D humic acid-carbon hybrid foam composed of multiple pores and pore walls, wherein pore walls contain single-layer or few-layer humic acid sheets chemically bonded by a carbon material at their edges and have a carbon material-to-humic acid weight ratio from 1/200 to 1/2, wherein the few-layer humic acid sheets have 2-10 layers of stacked substantially hexagonal carbon planes having an inter-plane spacing d 002  from 0.3354 nm to 0.40 nm as measured by X-ray diffraction and the single-layer or few-layer humic acid sheets contain 0.01% to 25% by weight of non-carbon elements wherein said humic acid is selected from oxidized humic acid, reduced humic acid, fluorinated humic acid, chlorinated humic acid, brominated humic acid, iodized humic acid, hydrogenated humic acid, nitrogenated humic acid, doped humic acid, chemically functionalized humic acid, or a combination thereof.

FIELD OF THE INVENTION

The present invention relates generally to the field of carbon/graphitefoams and, more particularly, to a new form of porous carbon materialherein referred to as an integral 3D humic acid-carbon hybrid foam and amethod of producing same.

BACKGROUND OF THE INVENTION

Carbon is known to have five unique crystalline structures, includingdiamond, fullerene (0-D nano graphitic material), carbon nano-tube orcarbon nano-fiber (1-D nano graphitic material), graphene (2-D nanographitic material), and graphite (3-D graphitic material).

The carbon nano-tube (CNT) refers to a tubular structure grown with asingle wall or multi-wall. Carbon nano-tubes (CNTs) and carbonnano-fibers (CNFs) have a diameter on the order of a few nanometers to afew hundred nanometers. Their longitudinal, hollow structures impartunique mechanical, electrical and chemical properties to the material.The CNT or CNF is a one-dimensional nano carbon or 1-D nano graphitematerial. However, CNTs are difficult to produce and are extremelyexpensive. Further, CNTs are known to be difficult to disperse in asolvent or water and difficult to mix with other materials. Thesecharacteristics have severely limited their scope of application.

A single-layer graphene sheet is composed of carbon atoms occupying atwo-dimensional hexagonal lattice. Multi-layer graphene is a plateletcomposed of more than one graphene plane. Individual single-layergraphene sheets and multi-layer graphene platelets are hereincollectively called nano graphene platelets (NGPs) or graphenematerials. NGPs include pristine graphene (essentially 99% of carbonatoms), slightly oxidized graphene (<5% by weight of oxygen), andgraphene oxide (≧5% by weight of oxygen).

NGPs have been found to have a range of unusual physical, chemical, andmechanical properties. For instance, graphene was found to exhibit thehighest intrinsic strength and highest thermal conductivity of allexisting materials. Although practical electronic device applicationsfor graphene (e.g., replacing Si as a backbone in a transistor) are notenvisioned to occur within the next 5-10 years, its application as anano filler in a composite material and an electrode material in energystorage devices is imminent. The availability of processable graphenesheets in large quantities is essential to the success in exploitingcomposite, energy, and other applications for graphene.

Our research group was among the first to discover graphene [B. Z. Jangand W. C. Huang, “Nano-scaled Graphene Plates,” U.S. patent applicationSer. No. 10/274,473, submitted on Oct. 21, 2002; now U.S. Pat. No.7,071,258 (Jul. 4, 2006)]. The processes for producing NGPs and NGPnanocomposites were previously reviewed by us [Bor Z. Jang and A Zhamu,“Processing of Nano Graphene Platelets (NGPs) and NGP Nanocomposites: AReview,” J. Materials Sci. 43 (2008) 5092-5101]. Four main prior-artapproaches have been followed to produce NGPs. Their advantages andshortcomings are briefly summarized as follows:

Approach 1: Chemical Formation and Reduction of Graphene Oxide (GO)

The first approach (FIG. 1) entails treating natural graphite powderwith an intercalant and an oxidant (e.g., concentrated sulfuric acid andnitric acid, respectively) to obtain a graphite intercalation compound(GIC) or, actually, graphite oxide (GO). [William S. Hummers, Jr., etal., Preparation of Graphitic Oxide, Journal of the American ChemicalSociety, 1958, p. 1339.] Prior to intercalation or oxidation, graphitehas an inter-graphene plane spacing of approximately 0.335 nm (L_(d)=½d₀₀₂=0.335 nm). With an intercalation and oxidation treatment, theinter-graphene spacing is increased to a value typically greater than0.6 nm. This is the first expansion stage experienced by the graphitematerial during this chemical route. The obtained GIC or GO is thensubjected to further expansion (often referred to as exfoliation) usingeither a thermal shock exposure or a solution-based,ultrasonication-assisted graphene layer exfoliation approach.

In the thermal shock exposure approach, the GIC or GO is exposed to ahigh temperature (typically 800-1,050° C.) for a short period of time(typically 15 to 60 seconds) to exfoliate or expand the GIC or GO forthe formation of exfoliated or further expanded graphite, which istypically in the form of a “graphite worm” composed of graphite flakesthat are still interconnected with one another. This thermal shockprocedure can produce some separated graphite flakes or graphene sheets,but normally the majority of graphite flakes remain interconnected.Typically, the exfoliated graphite or graphite worm is then subjected toa flake separation treatment using air milling, mechanical shearing, orultrasonication in water. Hence, approach 1 basically entails threedistinct procedures: first expansion (oxidation or intercalation),further expansion (or “exfoliation”), and separation.

In the solution-based separation approach, the expanded or exfoliated GOpowder is dispersed in water or aqueous alcohol solution, which issubjected to ultrasonication. It is important to note that in theseprocesses, ultrasonification is used after intercalation and oxidationof graphite (i.e., after first expansion) and typically after thermalshock exposure of the resulting GIC or GO (after second expansion).Alternatively, the GO powder dispersed in water is subjected to an ionexchange or lengthy purification procedure in such a manner that therepulsive forces between ions residing in the inter-planar spacesovercome the inter-graphene van der Waals forces, resulting in graphenelayer separations.

There are several major problems associated with this conventionalchemical production process:

-   -   (1) The process requires the use of large quantities of several        undesirable chemicals, such as sulfuric acid, nitric acid, and        potassium permanganate or sodium chlorate.    -   (2) The chemical treatment process requires a long intercalation        and oxidation time, typically 5 hours to five days.    -   (3) Strong acids consume a significant amount of graphite during        this long intercalation or oxidation process by “eating their        way into the graphite” (converting graphite into carbon dioxide,        which is lost in the process). It is not unusual to lose 20-50%        by weight of the graphite material immersed in strong acids and        oxidizers.    -   (4) The thermal exfoliation requires a high temperature        (typically 800-1,200° C.) and, hence, is a highly        energy-intensive process.    -   (5) Both heat- and solution-induced exfoliation approaches        require a very tedious washing and purification step. For        instance, typically 2.5 kg of water is used to wash and recover        1 gram of GIC, producing huge quantities of waste water that        need to be properly treated.    -   (6) In both the heat- and solution-induced exfoliation        approaches, the resulting products are GO platelets that must        undergo a further chemical reduction treatment to reduce the        oxygen content. Typically even after reduction, the electrical        conductivity of GO platelets remains much lower than that of        pristine graphene. Furthermore, the reduction procedure often        involves the utilization of toxic chemicals, such as hydrazine.    -   (7) Furthermore, the quantity of intercalation solution retained        on the flakes after draining may range from 20 to 150 parts of        solution by weight per 100 parts by weight of graphite flakes        (pph) and more typically about 50 to 120 pph. During the        high-temperature exfoliation, the residual intercalate species        retained by the flakes decompose to produce various species of        sulfuric and nitrous compounds (e.g., NO_(x) and SO_(x)), which        are undesirable. The effluents require expensive remediation        procedures in order not to have an adverse environmental impact.        Approach 2: Direct Formation of Pristine Nano Graphene Platelets

In 2002, our research team succeeded in isolating single-layer andmulti-layer graphene sheets from partially carbonized or graphitizedpolymeric carbons, which were obtained from a polymer or pitch precursor[B. Z. Jang and W. C. Huang, “Nano-scaled Graphene Plates,” U.S. patentapplication Ser. No. 10/274,473, submitted on Oct. 21, 2002; now U.S.Pat. No. 7,071,258 (Jul. 4, 2006)]. Mack, et al [“Chemical manufactureof nanostructured materials” U.S. Pat. No. 6,872,330 (Mar. 29, 2005)]developed a process that involved intercalating graphite with potassiummelt and contacting the resulting K-intercalated graphite with alcohol,producing violently exfoliated graphite containing NGPs. The processmust be carefully conducted in a vacuum or an extremely dry glove boxenvironment since pure alkali metals, such as potassium and sodium, areextremely sensitive to moisture and pose an explosion danger. Thisprocess is not amenable to the mass production of NGPs.

Approach 3: Epitaxial Growth and Chemical Vapor Deposition of NanoGraphene Sheets on Inorganic Crystal Surfaces

Small-scale production of ultra-thin graphene sheets on a substrate canbe obtained by thermal decomposition-based epitaxial growth and a laserdesorption-ionization technique. [Walt A. DeHeer, Claire Berger, PhillipN. First, “Patterned thin film graphite devices and method for makingsame” U.S. Pat. No. 7,327,000 B2 (Jun. 12, 2003)] Epitaxial films ofgraphite with only one or a few atomic layers are of technological andscientific significance due to their peculiar characteristics and greatpotential as a device substrate. However, these processes are notsuitable for mass production of isolated graphene sheets for compositematerials and energy storage applications.

Another process for producing graphene, in a thin film form (typically<2 nm in thickness), is the catalytic chemical vapor deposition process.This catalytic CVD involves catalytic decomposition of hydrocarbon gas(e.g. C₂H₄) on Ni or Cu surface to form single-layer or few-layergraphene. With Ni or Cu being the catalyst, carbon atoms obtained viadecomposition of hydrocarbon gas molecules at a temperature of800-1,000° C. are directly deposited onto Cu foil surface orprecipitated out to the surface of a Ni foil from a Ni—C solid solutionstate to form a sheet of single-layer or few-layer graphene (less than 5layers). The Ni- or Cu-catalyzed CVD process does not lend itself to thedeposition of more than 5 graphene planes (typically <2 nm) beyond whichthe underlying Ni or Cu layer can no longer provide any catalyticeffect. The CVD graphene films are extremely expensive.

Approach 4: The Bottom-Up Approach (Synthesis of Graphene from SmallMolecules)

Yang, et al. [“Two-dimensional Graphene Nano-ribbons,” J. Am. Chem. Soc.130 (2008) 4216-17] synthesized nano graphene sheets with lengths of upto 12 nm using a method that began with Suzuki-Miyaura coupling of1,4-diiodo-2,3,5,6-tetraphenyl-benzene with 4-bromophenylboronic acid.The resulting hexaphenylbenzene derivative was further derivatized andring-fused into small graphene sheets. This is a slow process that thusfar has produced very small graphene sheets.

Hence, an urgent need exists to have a new class of carbon nanomaterials that are comparable or superior to graphene in terms ofproperties, but can be produced more cost-effectively, faster, morescalable, and in a more environmentally benign manner. The productionprocess for such a new carbon nano material requires a reduced amount ofundesirable chemical (or elimination of these chemicals all together),shortened process time, less energy consumption, reduced or eliminatedeffluents of undesirable chemical species into the drainage (e.g.,sulfuric acid) or into the air (e.g., SO₂ and NO₂). Furthermore, oneshould be able to readily make this new nano material into a foamstructure that is relatively conductive thermally and electrically.

Generally speaking, a foam or foamed material is composed of pores (orcells) and pore walls (a solid material). The pores can beinterconnected to form an open-cell foam. As an example, graphene foamis composed of pores and pore walls that contain a graphene material.There are three major methods of producing graphene foams, which are alltedious, energy-intensive, and slow:

The first method is the hydrothermal reduction of graphene oxidehydrogel that typically involves sealing graphene oxide (GO) aqueoussuspension in a high-pressure autoclave and heating the GO suspensionunder a high pressure (tens or hundreds of atm) at a temperaturetypically in the range of 180-300° C. for an extended period of time(typically 12-36 hours). A useful reference for this method is givenhere: Y. Xu, et al. “Self-Assembled Graphene Hydrogel via a One-StepHydrothermal Process,” ACS Nano 2010, 4, 4324-4330. There are severalmajor issues associated with this method: (a) The high pressurerequirement makes it an impractical method for industrial-scaleproduction. For one thing, this process cannot be conducted on acontinuous basis. (b) It is difficult, if not impossible, to exercisecontrol over the pore size and the porosity level of the resultingporous structure. (c) There is no flexibility in terms of varying theshape and size of the resulting reduced graphene oxide (RGO) material(e.g. it cannot be made into a film shape). (d) The method involves theuse of an ultra-low concentration of GO suspended in water (e.g. 2mg/mL=2 g/L=2 kg/kL). With the removal of non-carbon elements (up to50%), one can only produce less than 2 kg of graphene material (RGO) per1000-liter suspension. Furthermore, it is practically impossible tooperate a 1000-liter reactor that has to withstand the conditions of ahigh temperature and a high pressure. Clearly, this is not a scalableprocess for mass production of porous graphene structures.

The second method is based on a template-assisted catalytic CVD process,which involves CVD deposition of graphene on a sacrificial template(e.g. Ni foam). The graphene material conforms to the shape anddimensions of the Ni foam structure. The Ni foam is then etched awayusing an etching agent, leaving behind a monolith of graphene skeletonthat is essentially an open-cell foam. A useful reference for thismethod is given here: Zongping Chen, et al., “Three-dimensional flexibleand conductive interconnected graphene networks grown by chemical vapourdeposition,” Nature Materials, 10 (June 2011) 424-428. There are severalproblems associated with such a process: (a) the catalytic CVD isintrinsically a very slow, highly energy-intensive, and expensiveprocess; (b) the etching agent is typically a highly undesirablechemical and the resulting Ni-containing etching solution is a source ofpollution. It is very difficult and expensive to recover or recycle thedissolved Ni metal from the etchant solution. (c) It is challenging tomaintain the shape and dimensions of the graphene foam without damagingthe cell walls when the Ni foam is being etched away. The resultinggraphene foam is typically very brittle and fragile. (d) The transportof the CVD precursor gas (e.g. hydrocarbon) into the interior of a metalfoam can be difficult, resulting in a non-uniform structure, sincecertain spots inside the sacrificial metal foam may not be accessible tothe CVD precursor gas.

The third method of producing graphene foam also makes use of asacrificial material (e.g. colloidal polystyrene particles, PS) that iscoated with graphene oxide sheets using a self-assembly approach. Forinstance, Choi, et al. prepared chemically modified graphene (CMG) paperin two steps: fabrication of free-standing PS/CMG films by vacuumfiltration of a mixed aqueous colloidal suspension of CMG and PS (2.0 μmPS spheres), followed by removal of PS beads to generate 3D macro-pores[B. G. Choi, et al., “3D Macroporous Graphene Frameworks forSupercapacitors with High Energy and Power Densities,” ACS Nano, 6(2012) 4020-4028.]. Choi, et al. fabricated well-ordered free-standingPS/CMG paper by filtration, which began with separately preparing anegatively charged CMG colloidal and a positively charged PS suspension.A mixture of CMG colloidal and PS suspension was dispersed in solutionunder controlled pH (=2), where the two compounds had the same surfacecharges (zeta potential values of +13±2.4 mV for CMG and +68±5.6 mV forPS). When the pH was raised to 6, CMGs (zeta potential=−29±3.7 mV) andPS spheres (zeta potential=+51±2.5 mV) were assembled due to theelectrostatic interactions and hydrophobic characteristics between them,and these were subsequently integrated into PS/CMG composite paperthrough a filtering process. This method also has several shortcomings:(a) This method requires very tedious chemical treatments of bothgraphene oxide and PS particles. (b) The removal of PS by toluene alsoleads to weakened macro-porous structures. (c) Toluene is a highlyregulated chemical and must be treated with extreme caution. (d) Thepore sizes are typically excessively big (e.g. several μm), too big formany useful applications.

The above discussion clearly indicates that every prior art method orprocess for producing graphene and graphene foams has majordeficiencies. Thus, it is an object of the present invention to providea new class of foam material that is thermally and electricallyconducting and mechanically robust and to provide a cost-effectivemethod of producing this class of foam.

Humic acid (HA) is an organic matter commonly found in soil and can beextracted from the soil using a base (e.g. KOH). HA can also beextracted, with a high yield, from a type of coal called leonardite,which is a highly oxidized version of lignite coal. HA extracted fromleonardite contains a number of oxygenated groups (e.g. carboxyl groups)located around the edges of the graphene-like molecular center (SP² coreof hexagonal carbon structure). This material is slightly similar tographene oxide (GO) which is produced by strong acid oxidation ofnatural graphite. HA has a typical oxygen content of 5% to 42% by weight(other major elements being carbon and hydrogen). HA, after chemical orthermal reduction, has an oxygen content of 0.01% to 5% by weight. Forclaim definition purposes in the instant application, humic acid (HA)refers to the entire oxygen content range, from 0.01% to 42% by weight.The reduced humic acid (RHA) is a special type of HA that has an oxygencontent of 0.01% to 5% by weight.

The present invention is directed at a new class of graphene-like 2Dmaterials (i.e. humic acid) that surprisingly can be used in acombination with carbon to form a hybrid foam. Thus, another object isto provide a cost-effective method of producing such a nano carbon foam(specifically, integral 3D humic acid-carbon hybrid foam) in largequantities. This method or process does not involve the use of anenvironmentally unfriendly chemical. This method enables the flexibledesign and control of the porosity level and pore sizes.

It is another object of the present invention to provide a humicacid-derived hybrid foam that exhibits a thermal conductivity,electrical conductivity, elastic modulus, and/or strength comparable toor greater than those of the conventional graphite foams, carbon foams,or graphene foams.

Yet another object of the present invention is to provide (a) a reducedhumic acid-based hybrid foam that contains essentially all carbon only(<5% by weight of non-carbon content, preferably <1%, and furtherpreferably <0.1%) and preferably have a meso-scaled pore size range(2-50 nm); and (b) humic acid foams that contain at least 5% by weight(typically from 5% to 42% by weight and most typically from 5% to 20%)of non-carbon elements that can be used for a broad array ofapplications.

Another object of the present invention is to provide products (e.g.devices) that contain an integral 3D humic acid-carbon foam of thepresent invention and methods of operating these products.

SUMMARY OF THE INVENTION

The present invention provides an integral 3D humic acid-carbon hybridfoam composed of multiple pores and pore walls, wherein the pore wallscontain single-layer or few-layer humic acid sheets chemically bonded bya carbon material at their edges and have a carbon material-to-humicacid weight ratio from 1/200 to 1/2, wherein the few-layer humic acidsheets have 2-10 layers of stacked substantially hexagonal carbon planeshaving an inter-plane spacing d₀₀₂ from 0.3354 nm to 0.40 nm as measuredby X-ray diffraction and said single-layer or few-layer humic acidsheets contain 0.01% to 25% by weight of non-carbon elements, whereinhumic acid is selected from oxidized humic acid, reduced humic acid,fluorinated humic acid, chlorinated humic acid, brominated humic acid,iodized humic acid, hydrogenated humic acid, nitrogenated humic acid,doped humic acid, chemically functionalized humic acid, or a combinationthereof.

The hybrid foam typically has a density from 0.005 to 1.7 g/cm³, aspecific surface area from 50 to 3,200 m²/g, a thermal conductivity ofat least 200 W/mK per unit of specific gravity, and/or an electricalconductivity no less than 2,000 S/cm per unit of specific gravity.Preferably, the hybrid foam has a density from 0.01 to 1.7 g/cm³ or anaverage pore size from 2 nm to 50 nm. In some preferred embodiments, thefoam has a specific surface area from 200 to 3,000 m²/g or a densityfrom 0.1 to 1.2 g/cm³.

In certain embodiments, the integral 3D humic acid-carbon hybrid foamcontains a content of non-carbon elements in the range of 0.01% to 20%by weight and the non-carbon elements include an element selected fromoxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, orboron.

In some embodiments, the pore walls contain fluorinated humic acid andsaid foam contains a fluorine content from 0.01% to 15% by weight. Incertain other embodiments, the pore walls contain oxidized humic acidand the foam contains an oxygen content from 0.01% to 20% by weight.

The 3D humic acid-carbon hybrid foam can be in a continuous-length rollsheet form having a thickness from 100 nm to 10 cm and a length of atleast 2 meters and may be produced by a roll-to-roll process.

In some embodiments, the 3D humic acid-carbon hybrid foam has an oxygencontent or non-carbon content less than 1% by weight, and said porewalls have an inter-planar spacing less than 0.35 nm, a thermalconductivity of at least 250 W/mK per unit of specific gravity, and/oran electrical conductivity no less than 2,500 S/cm per unit of specificgravity. Preferably, the hybrid foam has an oxygen content or non-carboncontent less than 0.01% by weight and the pore walls contain stackedhexagonal carbon planes having an inter-planar spacing less than 0.34nm, a thermal conductivity of at least 300 W/mK per unit of specificgravity, and/or an electrical conductivity no less than 3,000 S/cm perunit of specific gravity.

Further preferably, the foam has an oxygen content or non-carbon contentno greater than 0.01% by weight and the pore walls contain stackedhexagonal carbon planes having an inter-planar spacing less than 0.336nm, a thermal conductivity of at least 350 W/mK per unit of specificgravity, and/or an electrical conductivity no less than 3,500 S/cm perunit of specific gravity. Still more preferably, the foam has pore wallscontaining stacked hexagonal carbon planes having an inter-planarspacing less than 0.336 nm, a thermal conductivity greater than 400 W/mKper unit of specific gravity, and/or an electrical conductivity greaterthan 4,000 S/cm per unit of specific gravity. In some embodiments, thepore walls contain stacked hexagonal carbon planes having aninter-planar spacing less than 0.337 nm and a mosaic spread value lessthan 1.0.

Preferably, the pore walls contain a 3D network of interconnectedhexagonal carbon planes, or the foam contains meso-scaled pores having apore size from 2 nm to 50 nm.

The present invention also provides an oil-removing or oil-separatingdevice containing the 3D humic acid-carbon hybrid foam as anoil-absorbing element. Also provided is a solvent-removing orsolvent-separating device containing the 3D humic acid-carbon hybridfoam of as a solvent-absorbing or solvent-separating element.

The invention also provides a method to separate oil from water. Themethod comprises the steps of: (a) providing an oil-absorbing elementcomprising the integral 3D humic acid-carbon hybrid foam; (b) contactingan oil-water mixture with the element, which absorbs the oil from themixture; (c) retreating the element from the mixture and extracting theoil from the element; and (d) reusing the element.

Additionally, the invention provides a method to separate an organicsolvent from a solvent-water mixture or from a multiple-solvent mixture.The method comprises the steps of: (a) providing an organicsolvent-absorbing or solvent-separating element comprising the integral3D humic acid-carbon hybrid foam; (b) bringing the element in contactwith an organic solvent-water mixture or a multiple-solvent mixturecontaining a first solvent and at least a second solvent; (c) allowingthe element to absorb the organic solvent from the mixture or separatethe first solvent from the at least second solvent; (d) retreating theelement from the mixture and extracting the organic solvent or firstsolvent from the element; and (e) reusing the element.

Also provided is a thermal management device containing the 3D integralhumic acid-carbon hybrid foam as a heat spreading or heat dissipatingelement. The thermal management device may contain a device selectedfrom a heat exchanger, heat sink, heat pipe, high-conductivity insert,conductive plate between a heat sink and a heat source, heat-spreadingcomponent, heat-dissipating component, thermal interface medium, orthermoelectric or Peltier cooling device.

The present invention provides a method of producing an integral 3Dhumic acid-carbon hybrid foam. This method is stunningly simple. Themethod comprises: (A) forming a solid shape of humic acid-polymerparticle mixture; and (B) pyrolyzing the solid shape of humicacid-polymer particle mixture to thermally reduce said humic acid intoreduced humic acid sheets and, essentially concurrently, thermallyconvert the polymer into pores and carbon or graphite that bonds reducedhumic acid sheets to form the integral 3D humic acid-carbon hybrid foam.

Preferably, step (A) comprises: (i) dispersing humic acid in water or asolvent to form a suspension and dispersing multiple polymer particlesin this suspension to form a slurry; and (ii) dispensing the slurry andremoving water or solvent to form a solid shape of humic acid-polymerparticle mixture. Such a step enables humic acid molecules or sheets towrap around polymer particles (fully coated and embraced by humic acid).

Preferably, the integral 3D humic acid-carbon hybrid foam is in a film,sheet, paper, filament, rod, powder, ingot, or bulk form of essentiallyany reasonable shape.

The polymer particles preferably include plastic or rubber beads,pellets, spheres, wires, fibers, filaments, discs, ribbons, or rods,having a diameter or thickness from 10 nm to 10 mm (preferably from 100nm to 1 mm). In some embodiments, the polymer particles are selectedfrom solid particles of a thermoplastic, thermoset resin, rubber,semi-penetrating network polymer, penetrating network polymer, naturalpolymer, or a combination thereof.

In certain embodiments, the polymer particles contain a highcarbon-yield polymer selected from phenolic resin, poly furfurylalcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole,polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole,polybenzobisthiazole, poly(p-phenylene vinylene), polybenzimidazole,polybenzobisimidazole, a copolymer thereof, a polymer blend thereof, ora combination thereof.

In other embodiments, the polymer particles contain a low carbon-yieldpolymer selected from polyethylene, polypropylene, polybutylene,polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS),polyester, polyvinyl alcohol, poly vinylidiene fluoride (PVDF),polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), poly methylmethacrylate (PMMA), a copolymer thereof, a polymer blend thereof, or acombination thereof.

In the invented method, the step of pyrolyzing can include carbonizingthe polymer particles at a temperature from 200° C. to 2,500° C. toobtain reduced humic acid-carbon foam, or carbonizing the polymerparticles at a temperature from 200° C. to 2,500° C. to obtain reducedhumic acid-carbon foam and then graphitizing the reduced humicacid-carbon foam from 2,500° C. to 3,200° C. to obtain graphitized humicacid-carbon foam.

In certain embodiments, the shaping step includes melting the polymerparticles to form a polymer melt mixture with humic acid sheetsdispersed therein, forming the polymer melt mixture into a desired shapeand solidifying the desired shape into a humic acid-polymer compositestructure.

In certain embodiments, the shaping step includes dissolving the polymerparticles in a solvent to form a polymer solution mixture with humicacid sheets dispersed therein, forming the polymer solution mixture intoa desired shape, and removing the solvent to solidify the desired shapeinto a humic acid-polymer composite structure.

In desired embodiments where humic acid molecules or sheets wrap around(fully coat and embrace) the polymer particles, the shaping stepincludes forming the humic acid-coated polymer particles into acomposite shape selected from a rod, sheet, film, fiber, powder, ingot,or block form. Alternatively, the shaping step includes compacting humicacid-coated polymer particles into a porous green compact havingmacroscopic pores and then infiltrating or impregnating the pores withan additional carbon source material selected from a petroleum pitch,coal tar pitch, an aromatic organic material, a monomer, an organicpolymer, or a combination thereof. The organic polymer may contain ahigh carbon-yield polymer selected from phenolic resin, poly furfurylalcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole,polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole,polybenzobisthiazole, poly(p-phenylene vinylene), polybenzimidazole,polybenzobisimidazole, a copolymer thereof, a polymer blend thereof, ora combination thereof.

In desired embodiments where humic acid molecules or sheets wrap around(fully coat and embrace) the polymer particles, the shaping stepincludes forming a mass of said graphene-coated or graphene-embeddedpolymer particles into a compacted object. The compacted object may bein a form selected from a rod, sheet, film, fiber, powder, ingot, orblock.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A flow chart showing the most commonly used prior art process ofproducing highly oxidized graphene (NGPs) that entails tedious chemicaloxidation/intercalation, rinsing, and high-temperature exfoliationprocedures.

FIG. 2 A flow chart showing the presently invented process for producingintegral 3D humic acid-carbon hybrid foam.

FIG. 3 Schematic of the heat-induced conversion of polymer into carbon,which bonds humic acid sheets together to form a 3D HA-carbon hybridfoam. The compacted structure of humic acid-coated polymer particles isconverted into a highly porous structure.

FIG. 4(A) Thermal conductivity values vs. specific gravity of a 3Dintegral HA-carbon foam produced by the presently invented process, ameso-phase pitch-derived graphite foam, and a Ni foam-template assistedCVD graphene foam.

FIG. 4(B) Thermal conductivity values of 3D HA-carbon foam and thehydrothermally reduced GO graphene foam.

FIG. 5 Thermal conductivity values of 3D HA-carbon hybrid foam andpristine graphene foam (prepared by casting with a blowing agent andthen heat treating) plotted as a function of the final (maximum) heattreatment temperature.

FIG. 6 Electrical conductivity values of 3D HA-carbon foam and thehydrothermally reduced GO graphene foam.

FIG. 7 The amount of oil absorbed per gram of integral 3D HA-carbonhybrid foam, plotted as a function of the oxygen content in the foamhaving a porosity level of approximately 98% (oil separation fromoil-water mixture).

FIG. 8 The amount of oil absorbed per gram of integral 3D HA-carbonhybrid foam, plotted as a function of the porosity level (given the sameoxygen content).

FIG. 9 The amount of chloroform absorbed out of a chloroform-watermixture, plotted as a function of the degree of fluorination.

FIG. 10 Schematic of heat sink structures (2 examples).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Humic acid (HA) is an organic matter commonly found in soil and can beextracted from the soil using a base (e.g. KOH). HA can also beextracted from a type of coal called leonardite, which is a highlyoxidized version of lignite coal. HA extracted from leonardite containsa number of oxygenated groups (e.g. carboxyl groups) located around theedges of the graphene-like molecular center (SP² core of hexagonalcarbon structure). This material is slightly similar to graphene oxide(GO) which is produced by strong acid oxidation of natural graphite. HAhas a typical oxygen content of 5% to 42% by weight (other majorelements being carbon, hydrogen, and nitrogen). Example of a typicalhumic acid, having a variety of components including quinone, phenol,catechol and sugar moieties, is given in Scheme 1 below (source:Stevenson F. J. “Humus Chemistry: Genesis, Composition, Reactions,” JohnWiley & Sons, New York 1994).

The present invention provides an integral 3D humic acid-carbon hybridfoam and a method of producing such a hybrid foam. This method isstunningly simple, but effective, of low cost, and environmentallybenign. As schematically illustrated in FIG. 2, the method comprises:(A) forming a solid shape of humic acid-polymer particle mixture; and(B) pyrolyzing the solid shape of humic acid-polymer particle mixture tothermally reduce humic acid into reduced humic acid sheets and,essentially concurrently, thermally convert the polymer into pores andcarbon or graphite that bonds reduced humic acid sheets to form theintegral 3D humic acid-carbon hybrid foam.

Preferably, step (A) comprises: (i) dispersing humic acid in water or asolvent to form a suspension (or solution) and dispersing multiplepolymer particles in this suspension or solution to form a slurry; and(ii) dispensing the slurry and removing water or solvent to form a solidshape of humic acid-polymer particle mixture. Such a step enables humicacid molecules or sheets to wrap around polymer particles (polymerparticles being fully coated and embraced by humic acid). Humic acid(HA) is readily dissolved in water and a wide variety of polar solvents,such as methanol and ethanol.

Preferably, upon heat treatments, the solid shape is transformed into anintegral 3D humic acid-carbon hybrid foam, which can be in a film,sheet, paper, filament, rod, powder, ingot, or bulk form of essentiallyany desired shape.

The method can include forming humic acid-embraced particles into adesired shape of humic acid-polymer composite structure. This formingstep can be as simple as a compacting step that just mechanically packshumic acid-coated or embedded polymer particles into a desired shape.Alternatively, this forming step can entail melting the polymerparticles to form a polymer matrix with humic acid molecules or sheetsdispersed therein. Such a humic acid-polymer structure can be in anypractical shape or dimensions (fiber, rod, plate, cylinder, or anyregular shape or odd shape).

The humic acid-polymer compact or composite structure is then pyrolyzedto thermally reduce humic acid into reduced humic acid (RHA) and,concurrently, thermally convert the polymer into carbon or graphite thatbonds the reduced humic acid sheets together to form the integral 3DRHA-carbon hybrid foam. The non-carbon content of RHA can be variedbetween approximately 0.01% by weight and 5% by weight, depending uponthe maximum heat treatment temperature involved.

For the formation of the carbon component of the resulting humicacid-carbon hybrid foam, one can choose polymer particles that have ahigh carbon yield or char yield (e.g. >30% by weight of a polymer beingconverted to a solid carbon phase; instead of becoming part of avolatile gas). The high carbon-yield polymer may be selected fromphenolic resin, poly furfuryl alcohol, polyacrylonitrile, polyimide,polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole,polythiazole, polybenzothiazole, polybenzobisthiazole, poly(p-phenylenevinylene), polybenzimidazole, polybenzobisimidazole, a copolymerthereof, a polymer blend thereof, or a combination thereof. Whenpyrolyzed, particles of these polymers become porous, as illustrated inthe bottom portion of FIG. 3.

If a lower carbon content (higher humic acid proportion relative tocarbon proportion) and lower foam density (higher porosity level) aredesired in the HC-carbon hybrid foam, the polymer can contain a lowcarbon-yield polymer selected from polyethylene, polypropylene,polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene(ABS), polyester, polyvinyl alcohol, poly vinylidiene fluoride (PVDF),polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), poly methylmethacrylate (PMMA), a copolymer thereof, a polymer blend thereof, or acombination thereof. When pyrolyzed, particles of these polymers becomeporous, as illustrated in the middle portion of FIG. 3.

These polymers (both high and low carbon yields), when heated at atemperature of 300-2,500° C., are converted into a carbon material,which is preferentially nucleated near humic acid (HA) sheet edges. Sucha carbon material naturally bridges the gaps between HA sheets, forminginterconnected electron-conducting pathways. In actuality, the resultingHA-carbon hybrid foam is composed of integral 3D network ofcarbon-bonded HA sheets, enabling continuous transport of electrons andphonons (quantized lattice vibrations) between HA sheets or domainswithout interruptions. When further heated at a temperature higher than2,500° C., the carbon phase can get graphitized to further increase boththe electric conductivity and thermal conductivity. The amount ofnon-carbon elements is also decreased to typically below 1% by weight(down to 0.01%) if the graphitization time exceeds 1 hour.

It may be noted that an organic polymer typically contains a significantamount of non-carbon elements, which can be reduced or eliminated viaheat treatments. As such, pyrolyzation of a polymer causes the formationand evolution of volatile gas molecules, such as CO₂ and H₂O, which leadto the formation of pores in the resulting polymeric carbon phase.However, such pores also have a high tendency to get collapsed if thepolymer is not constrained when being carbonized (the carbon structurecan shrink while non-carbon elements are being released). We havesurprising discovered that the humic acid sheets wrapped around apolymer particle are capable of constraining the carbon pore walls frombeing collapsed. In the meantime, some carbon species also permeate tothe gaps between humic acid sheets where these species bond the humicacid sheets together. The pore sizes and pore volume (porosity level) ofthe resulting 3D integral humic acid-carbon foam mainly depend upon thestarting polymer size and the carbon yield of the polymer.

It may be further noted that a certain desired degree of hydrophilicitycan be imparted to the pore walls of the humic acid-carbon hybrid foamif the non-carbon element content (H and O) is from 2 to 20% by weight.These features enable separation of oil from water by selectivelyabsorbing oil from an oil-water mixture. In other words, such aHA-carbon hybrid foam material is capable of recovering oil from water,helping to clean up oil-spilled river, lake, or ocean. The oilabsorption capacity is typically from 50% to 500% of the foam's ownweight. This is a wonderfully useful material for environmentalprotection purposes.

If a high electrical or thermal conductivity is desired, the HA-carbonfoam can be subjected to graphitization treatment at a temperaturehigher than 2,500° C. The resulting material is particularly useful forthermal management applications (e.g. for use to make a finned heatsink, a heat exchanger, or a heat spreader).

It may be noted that the HA-carbon foam may be subjected to compressionduring and/or after the graphitization treatment. This operation enablesus to adjust the graphene sheet orientation and the degree of porosity.

In order to characterize the structure of the graphitic materialsproduced, X-ray diffraction patterns were obtained with an X-raydiffractometer equipped with CuKcv radiation. The shift and broadeningof diffraction peaks were calibrated using a silicon powder standard.The degree of graphitization, g, was calculated from the X-ray patternusing the Mering's Eq, d₀₀₂=0.3354 g+0.344 (1−g), where d₀₀₂ is theinterlayer spacing of graphite or graphene crystal in nm. This equationis valid only when d₀₀₂ is equal or less than approximately 0.3440 nm.In the present study, the graphene-like (HA or RHA) foam walls having ad₀₀₂ higher than 0.3440 nm reflects the presence of oxygen-containingfunctional groups (such as —OH, >O, and —COOH on graphene molecularplane surfaces or edges) that act as a spacer to increase theinter-graphene spacing.

Another structural index that can be used to characterize the degree ofordering of the stacked and bonded RHA planes in the foam walls ofgraphene and conventional graphite crystals is the “mosaic spread,”which is expressed by the full width at half maximum of a rocking curve(X-ray diffraction intensity) of the (002) or (004) reflection. Thisdegree of ordering characterizes the graphite or graphene crystal size(or grain size), amounts of grain boundaries and other defects, and thedegree of preferred grain orientation. A nearly perfect single crystalof graphite is characterized by having a mosaic spread value of 0.2-0.4.Most of our RHA walls have a mosaic spread value in this range of0.2-0.4 (if produced with a heat treatment temperature (HTT) no lessthan 2,500° C.). However, some values are in the range of 0.4-0.7 if theHTT is between 1,500 and 2,500° C., and in the range of 0.7-1.0 if theHTT is between 300 and 1,500° C.

In-depth studies using a combination of SEM, TEM, selected areadiffraction, X-ray diffraction, AFM, Raman spectroscopy, and FTIRindicate that the humic acid-carbon foam walls are composed of severallarge graphene planes (with length/width typically >>20 nm, moretypically >>100 nm, often >>1 μm, and, in many cases, >>10 μm). This isquite unexpected since the lateral dimensions (length and width) oforiginal humic acid sheets or molecules, prior to being heat treated,are typically <20 nm and more typically <10 nm. This implies that aplurality of HA sheets or molecules can be merged edge to edge throughcovalent bonds with one another, into a larger (longer or wider) sheet.

These large graphene-like planes also can be stacked and bonded alongthe thickness direction (crystallographic c-axis direction) oftenthrough not just the van der Waals forces (as in conventional graphitecrystallites), but also covalent bonds, if the final heat treatmenttemperature is lower than 2,500° C. In these cases, wishing not to belimited by theory, but Raman and FTIR spectroscopy studies appear toindicate the co-existence of sp² (dominating) and sp³ (weak butexisting) electronic configurations, not just the conventional sp² ingraphite.

The integral 3D HA-carbon hybrid foam is composed of multiple pores andpore walls, wherein the pore walls contain single-layer or few-layer HAsheets chemically bonded by a carbon material having a carbonmaterial-to-HA weight ratio from 1/100 to 1/2, wherein the few-layer HAsheets have 2-10 layers of stacked graphene-like HA planes having aninter-plane spacing d₀₀₂ from 0.3354 nm to 0.36 nm as measured by X-raydiffraction and the single-layer or few-layer graphene-like HA sheetscontain 0.01% to 25% by weight of non-carbon elements (more typically<15%). A plurality of single-layer or few-layer HA sheets embracing theunderlying polymer particles can overlap with one another to form astack of graphene-like sheets. The stack can have a thickness greaterthan 5 nm and, in some cases, greater than 10 nm.

The integral 3D HA-carbon hybrid foam typically has a density from 0.001to 1.7 g/cm³, a specific surface area from 50 to 3,000 m²/g, a thermalconductivity of at least 200 W/mK per unit of specific gravity, and/oran electrical conductivity no less than 2,000 S/cm per unit of specificgravity. In a preferred embodiment, the pore walls contain stackedgraphene-like RHA planes having an inter-planar spacing d₀₀₂ from 0.3354nm to 0.40 nm as measured by X-ray diffraction.

Many of the HA sheets can be merged edge to edge through covalent bondswith one another, into an integrated RHA entity. The gaps between thefree ends of those unmerged sheets or shorter merged sheets are bondedby the carbon phase converted from the polymer particles. Due to theseunique chemical composition (including oxygen or hydrogen content,etc.), morphology, crystal structure (including inter-planar spacing),and structural features (e.g. degree of orientations, few defects,chemical bonding and no gap between graphene-like sheets, andsubstantially no interruptions along graphene plane directions), theHA-carbon hybrid foam has a unique combination of outstanding thermalconductivity, electrical conductivity, mechanical strength, andstiffness (elastic modulus).

Thermal Management Applications

The aforementioned features and characteristics make the integral 3DHA-carbon hybrid foam an ideal element for a broad array of engineeringand biomedical applications. For instance, for thermal managementpurposes alone, the graphene-carbon foam can be used in the followingapplications:

-   -   a) The HA-carbon hybrid foam, being compressible and of high        thermal conductivity, is ideally suited for use as a thermal        interface material (TIM) that can be implemented between a heat        source and a heat spreader or between a heat source and a heat        sink.    -   b) The hybrid foam can be used as a heat spreader per se due to        its high thermal conductivity.    -   c) The hybrid foam can be used as a heat sink or heat        dissipating material due to his high heat-spreading capability        (high thermal conductivity) and high heat-dissipating capability        (large number of surface pores inducing massive air-convection        micro or nano channels).    -   d) The light weight (low density adjustable between 0.001 and        1.8 g/cm³), high thermal conductivity per unit specific gravity        or per unit of physical density, and high structural integrity        (HA sheets being bonded by carbon) make this hybrid foam an        ideal material for a durable heat exchanger.

The HA-carbon hybrid foam-based thermal management or heat dissipatingdevices include a heat exchanger, a heat sink (e.g. finned heat sink), aheat pipe, high-conductivity insert, thin or thick conductive plate(between a heat sink and a heat source), thermal interface medium (orthermal interface material, TIM), thermoelectric or Peltier coolingplate, etc.

A heat exchanger is a device used to transfer heat between one or morefluids; e.g. a gas and a liquid separately flowing in differentchannels. The fluids are typically separated by a solid wall to preventmixing. The presently invented graphene-carbon hybrid foam material isan ideal material for such a wall provided the foam is not a totallyopen-cell foam that allows for mixing of fluids. The presently inventedmethod enables production of both open-cell and closed-cell foamstructures. The high surface pore areas enable dramatically fasterexchange of heats between the two or multiple fluids.

Heat exchangers are widely used in refrigeration systems, airconditioning units, heaters, power stations, chemical plants,petrochemical plants, petroleum refineries, natural-gas processing, andsewage treatment. A well-known example of a heat exchanger is found inan internal combustion engine in which a circulating engine coolantflows through radiator coils while air flows past the coils, which coolsthe coolant and heats the incoming air. The solid walls (e.g. thatconstitute the radiator coils) are normally made of a high thermalconductivity material, such as Cu and Al. The presently inventedHA-carbon foam having either a higher thermal conductivity or higherspecific surface area is a superior alternative to Cu and Al, forinstance.

There are many types of heat exchangers that are commercially available:shell and tube heat exchanger, plate heat exchangers, plate and shellheat exchanger, adiabatic wheel heat exchanger, plate fin heatexchanger, pillow plate heat exchanger, fluid heat exchangers, wasteheat recovery units, dynamic scraped surface heat exchanger,phase-change heat exchangers, direct contact heat exchangers, andmicrochannel heat exchangers. Every one of these types of heatexchangers can take advantage of the exceptional high thermalconductivity and specific surface area of the presently invented foammaterial.

The presently invented solid HA-carbon foam can also be used in a heatsink. Heat sinks are widely used in electronic devices for heatdissipation purposes. The central processing unit (CPU) and battery in aportable microelectronic device (such as a notebook computer, tablet,and smart phone) are well-known heat sources. Typically, a metal orgraphite object (e.g. Cu foil or graphite foil) is brought into contactwith the hot surface and this object helps to spread the heat to anexternal surface or outside air (primarily by conduction and convectionand to a lesser extent by radiation). In most cases, a thin thermalinterface material (TIM) mediates between the hot surface of the heatsource and a heat spreader or a heat-spreading surface of a heat sink.(The presently invented HA-carbon foam can also be used as a TIM.)

A heat sink usually consists of a high-conductivity material structurewith one or more flat surfaces to ensure good thermal contact with thecomponents to be cooled, and an array of comb or fin like protrusions toincrease the surface contact with the air, and thus the rate of heatdissipation. A heat sink may be used in conjunction with a fan toincrease the rate of airflow over the heat sink. A heat sink can havemultiple fins (extended or protruded surfaces) to improve heat transfer.In electronic devices with limited amount of space, theshape/arrangement of fins must be optimized such that the heat transferdensity is maximized. Alternatively or additionally, cavities (invertedfins) may be embedded in the regions formed between adjacent fins. Thesecavities are effective in extracting heat from a variety of heatgenerating bodies to a heat sink.

Typically, an integrated heat sink comprises a heat collection member(core or base) and at least one heat dissipation member (e.g. a fin ormultiple fins) integral to the heat collection member (base) to form afinned heat sink. The fins and the core are naturally connected orintegrated together into a unified body without using an externallyapplied adhesive or mechanical fastening means to connect the fins tothe core. The heat collection base has a surface in thermal contact witha heat source (e.g. a LED), collects heat from this heat source, anddissipates heat through the fins into the air.

As illustrative examples, FIG. 10 provides a schematic of two heatsinks: 300 and 302. The first one contains a heat collection member (orbase member) 304 and multiple fins or heat dissipation members (e.g. fin306) connected to the base member 304. The base member 304 is shown tohave a heat collection surface 314 intended to be in thermal contactwith a heat source. The heat dissipation member or fin 306 is shown tohave at least a heat dissipation surface 320.

A particularly useful embodiment is an integrated radial heat sink 302comprising a radial finned heat sink assembly that comprises: (a) a base308 comprising a heat collection surface 318; and (b) a plurality ofspaced parallel planar fin members (e.g. 310, 312 as two examples)supported by or integral with the base 308, wherein the planar finmembers (e.g. 310) comprise the at least one heat dissipation surface322. Multiple parallel planar fin members are preferably equally spaced.

The presently invented HA-carbon hybrid foam, being highly elastic andresilient, is itself a good thermal interface material and a highlyeffective heat spreading element as well. In addition, thishigh-conductivity foam can also be used as an inserts for electroniccooling and for enhancing the heat removal from small chips to a heatsink. Because the space occupied by high conductivity materials is amajor concern, it is a more efficient design to make use of highconductivity pathways that can be embedded into a heat generating body.The elastic and highly conducting solid graphene foam herein disclosedmeets these requirements perfectly.

The high elasticity and high thermal conductivity make the presentlyinvented solid HA-carbon hybrid foam a good conductive thick plate to beplaced as a heat transfer interface between a heat source and a coldflowing fluid (or any other heat sink) to improve the coolingperformance. In such arrangement, the heat source is cooled under thethick HA-carbon foam plate instead of being cooled in direct contactwith the cooling fluid. The thick plate of HA-carbon foam cansignificantly improve the heat transfer between the heat source and thecooling fluid by way of conducting the heat current in an optimalmanner. No additional pumping power and no extra heat transfer surfacearea are required.

The solid HA-carbon foam is also an outstanding material to construct aheat pipe. A heat pipe is a heat transfer device that uses evaporationand condensation of a two-phase working fluid or coolant to transportlarge quantities of heat with a very small difference in temperaturebetween the hot and cold interfaces. A conventional heat pipe consistsof sealed hollow tube made of a thermally conductive metal such as Cu orAl, and a wick to return the working fluid from the evaporator to thecondenser. The pipe contains both saturated liquid and vapor of aworking fluid (such as water, methanol or ammonia), all other gasesbeing excluded. However, both Cu and Al are prone to oxidation orcorrosion and, hence, their performance degrades relatively fast overtime. In contrast, the solid HA-carbon foam is chemically inert and doesnot have these oxidation or corrosion issues. The heat pipe forelectronics thermal management can have a solid graphene foam envelopeand wick, with water as the working fluid. HA-carbon/methanol may beused if the heat pipe needs to operate below the freezing point ofwater, and HA-carbon/ammonia heat pipes may be used for electronicscooling in space.

Peltier cooling plates operate on the Peltier effect to create a heatflux between the junction of two different conductors of electricity byapplying an electric current. This effect is commonly used for coolingelectronic components and small instruments. In practice, many suchjunctions may be arranged in series to increase the effect to the amountof heating or cooling required. The solid graphene foam may be used toimprove the heat transfer efficiency.

Filtration and Fluid Absorption Applications

The solid HA-carbon foam can be made to contain microscopic pores (<2nm) or meso-scaled pores having a pore size from 2 nm to 50 nm. Thesolid HA-carbon hybrid foam can also be made to contain micron-scaledpores (1-500 μm). Based on well-controlled pore size alone, the instantHA-carbon foam can be an exceptional filter material for air or waterfiltration.

Further, the humic acid (HA) pore wall chemistry and carbon phasechemistry can be independently controlled to impart different amountsand/or types of functional groups to either or both of the HA sheets andthe carbon binder phase (e.g. as reflected by the percentage of O, F, N,H, etc. in the foam). In other words, the concurrent or independentcontrol of both pore sizes and chemical functional groups at differentsites of the internal structure provide unprecedented flexibility orhighest degree of freedom in designing and making HA-carbon hybrid foamsthat exhibit many unexpected properties, synergistic effects, and someunique combination of properties that are normally considered mutuallyexclusive (e.g. some part of the structure is hydrophobic and other parthydrophilic; or the foam structure is both hydrophobic and oleophilic).A surface or a material is said to be hydrophobic if water is repelledfrom this material or surface and that a droplet of water placed on ahydrophobic surface or material will form a large contact angle. Asurface or a material is said to be oleophilic if it has a strongaffinity for oils and not for water. The present method allows forprecise control over hydrophobicity, hydrophilicity, and oleophilicity.

The present invention also provides an oil-removing, oil-separating, oroil-recovering device, which contains the presently invented 3DHA-carbon hybrid foam as an oil-absorbing or oil-separating element.Also provided is a solvent-removing or solvent-separating devicecontaining the 3D HA-carbon hybrid foam as a solvent-absorbing element.

A major advantage of using the instant HA-carbon hybrid foam as anoil-absorbing element is its structural integrity. Due to the notionthat HA sheets are chemically bonded by the carbon material, theresulting foam would not get disintegrated upon repeated oil absorptionoperations. In contrast, we have discovered that graphene-basedoil-absorbing elements prepared by hydrothermal reduction,vacuum-assisted filtration, or freeze-drying get disintegrated afterabsorbing oil for 2 or 3 times. There is just nothing (other than weakvan der Waals forces existing prior to first contact with oil) to holdthese otherwise separated graphene sheets together. Once these graphenesheets are wetted by oil, they no longer are able to return to theoriginal shape of the oil-absorbing element.

Another major advantage of the instant technology is the flexibility indesigning and making oil-absorbing elements that are capable ofabsorbing oil up to an amount as high as 400 times of its own weight yetstill maintaining its structural shape (without significant expansion).This amount depends upon the specific pore volume of the foam, which canbe controlled mainly by the ratio between the amount of original carrierpolymer particles and the amount of HA molecules or sheets prior to theheat treatment.

The invention also provides a method to separate/recover oil from anoil-water mixture (e.g. oil-spilled water or waste water from oil sand).The method comprises the steps of (a) providing an oil-absorbing elementcomprising an integral HA-carbon hybrid foam; (b) contacting anoil-water mixture with the element, which absorbs the oil from themixture; and (c) retreating the oil-absorbing element from the mixtureand extracting the oil from the element. Preferably, the methodcomprises a further step of (d) reusing the element.

Additionally, the invention provides a method to separate an organicsolvent from a solvent-water mixture or from a multiple-solvent mixture.The method comprises the steps of (a) providing an organicsolvent-absorbing element comprising an integral HA-carbon hybrid foam;(b) bringing the element in contact with an organic solvent-watermixture or a multiple-solvent mixture containing a first solvent and atleast a second solvent; (c) allowing this element to absorb the organicsolvent from the mixture or absorb the first solvent from the at leastsecond solvent; and (d) retreating the element from the mixture andextracting the organic solvent or first solvent from the element.Preferably, the method contains an additional step (e) of reusing thesolvent-absorbing element.

The following examples are used to illustrate some specific detailsabout the best modes of practicing the instant invention and should notbe construed as limiting the scope of the invention.

Example 1: Production of Humic Acid-Carbon Foam from HA-CoatedPolypropylene (PP) Particles

One experiment entails dispersing 5% by weight of PP powder in a humicacid-water solution (5% HA) to obtain a slurry. The slurry was thenspray-dried to form powder of HA-coated PP particles. The HA-coated PPparticles were then compacted in a mold cavity to form a green compact,which was then heat-treated in a sealed crucible at 350° C. and then at600° C. for 2 hours to produce an integral HA-carbon hybrid foam.

Although polypropylene (PP) is herein used as an example, the solidpolymer particles for HA-carbon hybrid foam production are not limitedto PP. It could be any polymer (thermoplastic, thermoset, rubber, wax,mastic, gum, organic resin, etc.) provided the polymer can be made intoa particulate form (fine powder particles having a diameter preferablyin the range of 10 nm-10 μm, further preferably 20 nm-1 μm). It may benoted that un-cured or partially cured thermosetting resins (such asepoxide and imide-based oligomers or rubber) can be made into a particleform at room temperature or lower (e.g. cryogenic temperature). Hence,even partially cured thermosetting resin particles can be used as solidpolymer particles.

Example 2: Humic Acid-Carbon Hybrid Foam Using ABS as the Solid PolymerParticles

In an experiment, 100 grams of ABS powder, as solid polymer particles,were mixed into a humic acid-ethanol solution to form a slurry. Theslurry was cast on a glass surface to form HA-polymer films (20-200 μmthick), which were then carbonized to prepare HA-carbon foam samplesunder different temperature and compression conditions.

Example 3: Production of Humic Acid-Carbon Hybrid Foam from HA-CoatedPolyacrylonitrile (PAN) Fibers (as Solid Polymer Particles)

In one example, PAN fiber segments (2 mm long as the polymer particles)were dispersed in a HA-methanol solution to form a slurry, which wasoven dried to form a mass of HA-coated PAN fiber powder. The HA-coatedPAN fibers were then compacted and melted together to form severalcomposite films. The films were subjected to heat treatments at 250° C.for 1 hour (in room air), 350° C. for 2 hours, and 1,000° C. for 2 hours(under an argon gas atmosphere) to obtain RHA-carbon foam layers. Halfof the carbonized foam layers were then heated to 2,850° C. andmaintained at this temperature for 0.5 hours to obtain graphitizedRHA-carbon foam.

Example 4: Particles of Cured Phenolic Resin as the Polymer Particles

Particles of cured phenolic resin were dispersed in a HA-watersuspension to form a slurry, which was spray-dried to form a slurry. Amass of HA-coated resin particles was compressed to form a greencompact, which was then infiltrated with a small amount of petroleumpitch. Separately, another green compact of HA-coated resin particleswas prepared under comparable conditions, but no pitch infiltration wasattempted. The two compacts were then subjected to identical pyrolysistreatments.

Example 5: Polyethylene (PE) and Nylon 6/6 Beads as the Solid PolymerParticles

Slurry coating and drying was used to prepare HA-coated polymerparticles. Subsequently, a mass of HA-coated PE pellets and a mass ofHA-coated nylon beads were separately compacted in a mold cavity andbriefly heated above the melting point of PE or nylon and then rapidlycooled to form two green compacts. For comparison purposes, twocorresponding compacts were prepared from a mass of un-coated PE pelletsand a mass of un-coated nylon beads. These 4 compacts were thensubjected to pyrolyzation (by heating the compacts in a chamber from100° C. to 650° C.). The results were very surprising. The compacts ofHA-coated polymer particles were found to be converted tographene-carbon hybrid foam structures having dimensions comparable tothe dimensions of the original compacts (3 cm×3 cm×0.5 cm). SEMexamination of these structures indicates that carbon phases are presentnear the edges of HA sheets and these carbon phases act to bond the HAsheets together. The carbon-bonded HA sheets form a skeleton ofHA-carbon hybrid pore walls having pores being present in what used tobe the space occupied by the original polymer particles, asschematically illustrated in FIG. 3.

In contrast, the two compacts from un-coated pellets or beads shrank tobecome essentially two solid masses of carbon having a volumeapproximately 15%-20% of the original compact volumes. These highlyshrunk solid masses are practically pore-free carbon materials; they arenot a foam material.

Examples 6: Micron-Sized Rubber Particles as the Solid Polymer Particles

The experiment began with preparation of micron-sized rubber particles.A mixture of methylhydro dimethyl-siloxane polymer (20 g) andpolydimethylsiloxane, vinyldimethyl terminated polymer (30 g) wasobtained by using a homogenizer under ambient conditions for 1 minute.Tween 80 (4.6 g) was added and the mixture was homogenized for 20seconds. Platinum-divinyltetramethyldisiloxane complex (0.5 g in 15 gmethanol) was added and mixed for 10 seconds. This mixture was added to350 g of distilled water and a stable latex was obtained byhomogenization for 15 minutes. The latex was heated to 60° C. for 15hours. The latex was then de-emulsified with anhydrous sodium sulfate(20 g) and the silicone rubber particles were obtained by filtrationunder a vacuum, washing with distilled water, and drying under vacuum at25° C. The particle size distribution of the resulting rubber particleswas 3-11 μm.

Humic acid-coated rubber particles were obtained by spray-drying ofHA-water-rubber slurry. The HA-coated rubber particles were then mixedwith 5% by wt. of petroleum pitch (as a binder) and mechanicallycompacted together to form several composite sheets. The compositesheets were then subjected to heat treatments at 350° C. for 1 hour,650° C. for 2 hours, and 1,000° C. for 1 hour in a tube furnace toobtain HA-carbon foam layers.

Examples 7: Preparation of Fluorinated HA-Carbon Foams

In a typical procedure, a sheet of HA-carbon hybrid was fluorinated byvapors of chlorine trifluoride in a sealed autoclave reactor to yieldfluorinated HA-carbon hybrid film. Different durations of fluorinationtime were allowed for achieving different degrees of fluorination.Sheets of fluorinated HA-carbon foam were then separately immersed incontainers each containing a chloroform-water mixture. We observed thatthese foam sheets selectively absorb chloroform from water and theamount of chloroform absorbed increases with the degree of fluorinationuntil the fluorine content reaches 7.2% by wt. (FIG. 9).

Example 8: Preparation of Nitrogenated HA-Carbon Foams

Several pieces of HA-carbon foam prepared in Example 3 were immersed ina 30% H₂O₂-water solution for a period of 2-48 hours to obtain oxidizedHA-carbon foams, having a controlled oxygen content of 2-25% by weight.

Some oxidized HA-carbon foam samples were mixed with differentproportions of urea and the mixtures were heated in a microwave reactor(900 W) for 0.5 to 5 minutes. The products were washed several timeswith deionized water and vacuum dried. The products obtained werenitrogenated HA-carbon foam. The nitrogen contents were from 3% to 17.5wt. %, as measured by elemental analysis.

It may be noted that different functionalization treatments of theHA-carbon hybrid foam were for different purposes. For instance,oxidized HA-carbon hybrid foam structures are particularly effective asan absorber of oil from an oil-water mixture (i.e. oil spilled on waterand then mixed together). In this case, the integral 3D HA (0-15% by wt.oxygen)-carbon foam structures are both hydrophobic and oleophilic (FIG.7 and FIG. 8). A surface or a material is said to be hydrophobic ifwater is repelled from this material or surface and that a droplet ofwater placed on a hydrophobic surface or material will form a largecontact angle. A surface or a material is said to be oleophilic if ithas a strong affinity for oils and not for water.

Different contents of O, F, and/or N also enable the presently inventedHA-carbon hybrid foams to absorb different organic solvents from water,or to separate one organic solvent from a mixture of multiple solvents.

Comparative Example 1: Graphene Via Hummer's Process and Carbonizationof Graphene-Polymer Composite

Graphite oxide as prepared by oxidation of graphite flakes with sulfuricacid, nitrate, and permanganate according to the method of Hummers [U.S.Pat. No. 2,798,878, Jul. 9, 1957]. Upon completion of the reaction, themixture was poured into deionized water and filtered. The graphite oxidewas repeatedly washed in a 5% solution of HCl to remove most of thesulphate ions. The sample was then washed repeatedly with deionizedwater until the pH of the filtrate was neutral. The slurry wasspray-dried and stored in a vacuum oven at 60° C. for 24 hours. Theinterlayer spacing of the resulting laminar graphite oxide wasdetermined by the Debey-Scherrer X-ray technique to be approximately0.73 nm (7.3 A). A sample of this material was subsequently transferredto a furnace pre-set at 650° C. for 4 minutes for exfoliation and heatedin an inert atmosphere furnace at 1200° C. for 4 hours to create a lowdensity powder comprised of few-layer reduced graphene oxide (RGO).Surface area was measured via nitrogen adsorption BET. This powder wassubsequently dry mixed at a 1%-25% loading level with ABS, PE, PP, andnylon pellets, respectively, and compounded using a 25 mm twin screwextruder to form composite sheets. These composite sheets were thenpyrolyzed.

Comparative Example 2: Preparation of Single-Layer Graphene Oxide (GO)Sheets from Meso-Carbon Micro-Beads (MCMBs) and then Production ofGraphene Foam Layers from GO Sheets

Meso-carbon microbeads (MCMBs) were supplied from China Steel ChemicalCo., Kaohsiung, Taiwan. This material has a density of about 2.24 g/cm³with a median particle size of about 16 μm. MCMB (10 grams) wereintercalated with an acid solution (sulfuric acid, nitric acid, andpotassium permanganate at a ratio of 4:1:0.05) for 48-96 hours. Uponcompletion of the reaction, the mixture was poured into deionized waterand filtered. The intercalated MCMBs were repeatedly washed in a 5%solution of HCl to remove most of the sulphate ions. The sample was thenwashed repeatedly with deionized water until the pH of the filtrate wasno less than 4.5. The slurry was then subjected ultrasonication for10-100 minutes to produce GO suspensions. TEM and atomic forcemicroscopic studies indicate that most of the GO sheets weresingle-layer graphene when the oxidation treatment exceeded 72 hours,and 2- or 3-layer graphene when the oxidation time was from 48 to 72hours.

The GO sheets contain oxygen proportion of approximately 35%-47% byweight for oxidation treatment times of 48-96 hours. GO sheets weresuspended in water. Baking soda (5-20% by weight), as a chemical blowingagent, was added to the suspension just prior to casting. The suspensionwas then cast onto a glass surface. Several samples were cast, somecontaining a blowing agent and some not. The resulting GO films, afterremoval of liquid, have a thickness that can be varied fromapproximately 10 to 500 μm. Several sheets of the GO film, with orwithout a blowing agent, were then subjected to heat treatments thatinvolve a heat temperature of 80-500° C. for 1-5 hours, which generateda graphene foam structure.

Comparative Example 3: Preparation of Pristine Graphene Foam (0% Oxygen)

Recognizing the possibility of the high defect population in GO sheetsacting to reduce the conductivity of individual graphene plane, wedecided to study if the use of pristine graphene sheets (non-oxidizedand oxygen-free, non-halogenated and halogen-free, etc.) can lead to agraphene foam having a higher thermal conductivity. Pristine graphenesheets were produced by using the direct ultrasonication process (alsoknown as the liquid-phase exfoliation in the art).

In a typical procedure, five grams of graphite flakes, ground toapproximately 20 μm or less in sizes, were dispersed in 1,000 mL ofdeionized water (containing 0.1% by weight of a dispersing agent, Zonyl®FSO from DuPont) to obtain a suspension. An ultrasonic energy level of85 W (Branson S450 Ultrasonicator) was used for exfoliation, separation,and size reduction of graphene sheets for a period of 15 minutes to 2hours. The resulting graphene sheets are pristine graphene that havenever been oxidized and are oxygen-free and relatively defect-free.There are no other non-carbon elements.

Various amounts (1%-30% by weight relative to graphene material) ofchemical bowing agents (N, N-Dinitroso pentamethylene tetramine or 4.4′-Oxybis (benzenesulfonyl hydrazide) were added to a suspensioncontaining pristine graphene sheets and a surfactant. The suspension wasthen cast onto a glass surface. Several samples were cast, including onethat was made using CO₂ as a physical blowing agent introduced into thesuspension just prior to casting. The resulting graphene films, afterremoval of liquid, have a thickness that can be varied fromapproximately 10 to 100 μm. The graphene films were then subjected toheat treatments at a temperature of 80-1,500° C. for 1-5 hours, whichgenerated a graphene foam.

Comparative Example 4: CVD Graphene Foams on Ni Foam Templates

The procedure was adapted from that disclosed in open literature: Chen,Z. et al. “Three-dimensional flexible and conductive interconnectedgraphene networks grown by chemical vapor deposition,” Nat. Mater. 10,424-428 (2011). Nickel foam, a porous structure with an interconnected3D scaffold of nickel was chosen as a template for the growth ofgraphene foam. Briefly, carbon was introduced into a nickel foam bydecomposing CH₄ at 1,000° C. under ambient pressure, and graphene filmswere then deposited on the surface of the nickel foam. Due to thedifference in the thermal expansion coefficients between nickel andgraphene, ripples and wrinkles were formed on the graphene films. Inorder to recover (separate) graphene foam, Ni frame must be etched away.Before etching away the nickel skeleton by a hot HCl (or FeCl₃)solution, a thin layer of poly(methyl methacrylate) (PMMA) was depositedon the surface of the graphene films as a support to prevent thegraphene network from collapsing during nickel etching. After the PMMAlayer was carefully removed by hot acetone, a fragile graphene foamsample was obtained. The use of the PMMA support layer is critical topreparing a free-standing film of graphene foam; only a severelydistorted and deformed graphene foam sample was obtained without thePMMA support layer. This is a tedious process that is notenvironmentally benign and is not scalable.

Comparative Example 5: Conventional Graphitic Foam from Pitch-BasedCarbon Foams

Pitch powder, granules, or pellets are placed in a aluminum mold withthe desired final shape of the foam. Mitsubishi ARA-24 meso-phase pitchwas utilized. The sample is evacuated to less than 1 torr and thenheated to a temperature approximately 300° C. At this point, the vacuumwas released to a nitrogen blanket and then a pressure of up to 1,000psi was applied. The temperature of the system was then raised to 800°C. This was performed at a rate of 2 degree C./min. The temperature washeld for at least 15 minutes to achieve a soak and then the furnacepower was turned off and cooled to room temperature at a rate ofapproximately 1.5 degree C./min with release of pressure at a rate ofapproximately 2 psi/min. Final foam temperatures were 630° C. and 800°C. During the cooling cycle, pressure is released gradually toatmospheric conditions. The foam was then heat treated to 1050° C.(carbonized) under a nitrogen blanket and then heat treated in separateruns in a graphite crucible to 2500° C. and 2800° C. (graphitized) inArgon.

Comparative Example 6: Graphene Foams from Hydrothermally ReducedGraphene Oxide

For comparison, a self-assembled graphene hydrogel (SGH) sample wasprepared by a one-step hydrothermal method. In a typical procedure, theSGH can be easily prepared by heating 2 mg/mL of homogeneous grapheneoxide (GO) aqueous dispersion sealed in a Teflon-lined autoclave at 180°C. for 12 h. The SGH containing about 2.6% (by weight) graphene sheetsand 97.4% water has an electrical conductivity of approximately 5×10⁻³S/cm. Upon drying and heat treating at 1,500° C., the resulting graphenefoam exhibits an electrical conductivity of approximately 1.5×10⁻¹ S/cm,which is 2 times lower than those of the presently invented graphenefoams produced by heat treating at the same temperature.

Example 9: Thermal and Mechanical Testing of Various Graphene Foams andConventional Graphite Foam

Samples from various conventional carbon or graphene foam materials weremachined into specimens for measuring the thermal conductivity. The bulkthermal conductivity of meso-phase pitch-derived foam ranged from 67W/mK to 151 W/mK. The density of the samples was from 0.31-0.61 g/cm³.When weight is taken into account, the specific thermal conductivity ofthe pitch derived foam is approximately 67/0.31=216 and 151/0.61=247.5W/mK per specific gravity (or per physical density).

The compression strength of the samples having an average density of0.51 g/cm³ was measured to be 3.6 MPa and the compression modulus wasmeasured to be 74 MPa. By contrast, the compression strength andcompressive modulus of the presently invented RHA-carbon foam sampleshaving a comparable physical density are 6.1 MPa and 110 MPa,respectively.

Shown in FIG. 4(A) are the thermal conductivity values vs. specificgravity of the 3D HA-carbon foam, meso-phase pitch-derived graphitefoam, and Ni foam template-assisted CVD graphene foam. These dataclearly demonstrate the following unexpected results:

-   -   1) The 3D integral HA-carbon foams produced by the presently        invented process exhibit significantly higher thermal        conductivity as compared to both meso-phase pitch-derived        graphite foam and Ni foam template-assisted CVD graphene, given        the same physical density.    -   2) This is quite surprising in view of the notion that CVD        graphene is essentially pristine graphene that has never been        exposed to oxidation and should have exhibited a high thermal        conductivity compared to our HA-carbon hybrid foam. The carbon        phase of the hybrid foam is in general of low degree of        crystallinity (some being amorphous carbon) and, thus, has much        lower thermal or electrical conductivity as compared with        graphene alone. However, when the carbon phase is coupled with        RHA sheets to form an integral structure produced by the        presently invented method, the resulting hybrid foam exhibits a        higher thermal conductivity as compared to an all-pristine        graphene foam. These exceptionally high thermal conductivity        values observed with the RHA-carbon hybrid foams herein produced        are much to our surprise. This is likely due to the observation        that the otherwise isolated RHA sheets are now bonded by a        carbon phase, providing a bridge for the uninterrupted transport        of electrons and phonons.    -   3) The specific conductivity of the presently invented hybrid        foam materials exhibits values from 250 to 500 W/mK per unit of        specific gravity; but those of other types of foam materials are        typically lower than 250 W/mK per unit of specific gravity.    -   4) Summarized in FIG. 5 are thermal conductivity data for a        series of 3D HA-carbon foams and a series of pristine        graphene-derived foams, both plotted over the final (maximum)        heat treatment temperatures. In both types of materials, the        thermal conductivity increases monotonically with the final HTT.        However, the presently invented process enables the        cost-effective and environmentally benign production of        HA-carbon foams that outperform pristine graphene foams. This is        another unexpected result.    -   5) FIG. 4(B) shows the thermal conductivity values of the        presently invented hybrid foam and hydrothermally reduced GO        graphene foam. Electrical conductivity values of 3D HA-carbon        foam and the hydrothermally reduced GO graphene foam are shown        in FIG. 6. These data further support the notion that, given the        same amount of solid material, the presently invented HA-carbon        foam is intrinsically most conducting, reflecting the        significance of continuity in electron and phonon transport        paths. The carbon phase bridges the gaps or interruptions        between HA sheets.

Example 10: Characterization of Various HA-Carbon Foams, Graphene Foamsand Conventional Graphite Foam

The internal structures (crystal structure and orientation) of severalseries of HA-carbon foam materials were investigated using X-raydiffraction. The X-ray diffraction curve of natural graphite typicallyexhibits a peak at approximately 2θ=26°, corresponds to aninter-graphene spacing (d₀₀₂) of approximately 0.3345 nm. The RHA wallsof the hybrid foam materials exhibit a d₀₀₂ spacing typically from0.3345 nm to 0.40 nm, but more typically up to 0.34 nm.

With a heat treatment temperature of 2,750° C. for the foam structureunder compression for one hour, the d₀₀₂ spacing is decreased toapproximately to 0.3354 nm, identical to that of a graphite singlecrystal. In addition, a second diffraction peak with a high intensityappears at 2θ=55° corresponding to X-ray diffraction from (004) plane.The (004) peak intensity relative to the (002) intensity on the samediffraction curve, or the I(004)/I(002) ratio, is a good indication ofthe degree of crystal perfection and preferred orientation ofgraphene-like planes. The (004) peak is either non-existing orrelatively weak, with the I(004)/I(002) ratio <0.1, for all graphiticmaterials heat treated at a temperature lower than 2,800° C. TheI(004)/I(002) ratio for the graphitic materials heat treated at3,000-3,250° C. (e.g., highly oriented pyrolytic graphite, HOPG) is inthe range of 0.2-0.5. In contrast, a graphene foam prepared with a finalHTT of 2,750° C. for one hour exhibits a I(004)/I(002) ratio of 0.78 anda Mosaic spread value of 0.21, indicating the pore walls being apractically perfect graphite single crystal with a good degree ofpreferred orientation (if prepared under a compression force).

The “mosaic spread” value is obtained from the full width at halfmaximum of the (002) reflection in an X-ray diffraction intensity curve.This index for the degree of ordering characterizes the graphite orgraphene crystal size (or grain size), amounts of grain boundaries andother defects, and the degree of preferred grain orientation. A nearlyperfect single crystal of graphite is characterized by having a mosaicspread value of 0.2-0.4. Some of our graphene foams have a mosaic spreadvalue in this range of 0.3-0.6 when produced using a final heattreatment temperature no less than 2,500° C.

The following are a summary of some of the more significant results:

-   -   1) The presently invented HA-carbon hybrid foam materials        typically exhibit significantly higher structural integrity        (e.g. compression strength, elasticity, and resiliency) and        higher thermal and electrical conductivities as compared to        their graphene counterparts produced by the conventional, prior        art methods.    -   2) It is of significance to point out that all the prior art        processes for producing graphite foams or graphene foams appear        to provide only macro-porous foams having a physical density in        the range of approximately 0.2-0.6 g/cm³, with pore sizes being        typically too large (e.g. from 20 to 300 μm) for most of the        intended applications. In contrast, the instant invention        provides processes that generate HA-carbon foams having a        density that can be as low as 0.001 g/cm³ and as high as 1.7        g/cm³. The pore sizes can be varied from microscopic (<2 nm),        through meso-scaled (2-50 nm), and up to macro-scaled (e.g. from        1 to 500 μm). This level of flexibility and versatility in        designing various types of HA-carbon foams is unprecedented and        un-matched by any prior art process.    -   3) The presently invented method also allows for convenient and        flexible control over the chemical composition (e.g. F, O, and N        contents, etc.) of foams, responsive to various application        needs (e.g. oil recovery from oil-contaminated water, separation        of an organic solvent from water or other solvents, heat        dissipation, etc.).

In conclusion, we have successfully developed an absolutely new, novel,unexpected, and patently distinct class of highly conducting humicacid-carbon hybrid foam materials, devices, and related processes ofproduction. The chemical composition (% of oxygen, fluorine, and othernon-carbon elements), structure (crystal perfection, grain size, defectpopulation, etc.), crystal orientation, morphology, process ofproduction, and properties of this new class of foam materials arefundamentally different and patently distinct from meso-phasepitch-derived graphite foam, CVD graphene-derived foam, and graphenefoams from hydrothermal reduction of GO.

We claim:
 1. An integral 3D humic acid-carbon hybrid foam composed ofmultiple pores and pore walls, wherein said pore walls containsingle-layer or few-layer humic acid sheets chemically bonded by acarbon material at their edges and have a carbon material-to-humic acidweight ratio from 1/200 to 1/2, wherein few-layer is defined as havingtwo to ten atomic layers and wherein said few-layer humic acid sheetshave stacked substantially hexagonal carbon planes having an inter-planespacing d₀₀₂ from 0.3354 nm to 0.40 nm as measured by X-ray diffractionand said single-layer or few-layer humic acid sheets contain 0.01% to25% by weight of non-carbon elements wherein said humic acid is selectedfrom oxidized humic acid, reduced humic acid, fluorinated humic acid,chlorinated humic acid, brominated humic acid, iodized humic acid,hydrogenated humic acid, nitrogenated humic acid, doped humic acid,chemically functionalized humic acid, or a combination thereof.
 2. Theintegral 3D humic acid-carbon hybrid foam of claim 1, wherein saidhybrid foam has a density from 0.005 to 1.7 g/cm³, a specific surfacearea from 50 to 3,200 m²/g, a thermal conductivity from 200 to 400 W/mkper unit of specific gravity, and/or an electrical conductivity from2,000 to 4000 S/cm per unit of specific gravity.
 3. The integral 3Dhumic acid-carbon hybrid foam of claim 1, wherein said hybrid foam has adensity from 0.01 to 1.7 g/cm³ or an average pore size from 2 nm to 50nm.
 4. The integral 3D humic acid-carbon hybrid foam of claim 1, whereinsaid foam contains a content of non-carbon elements in the range of0.01% to 20% by weight and said non-carbon elements include an elementselected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen,hydrogen, or boron.
 5. The integral 3D humic acid-carbon hybrid foam ofclaim 1, wherein said pore walls contain fluorinated humic acid and saidfoam contains a fluorine content from 0.01% to 15% by weight.
 6. The 3Dhumic acid-carbon hybrid foam of claim 1, wherein said pore wallscontain oxidized humic acid and said foam contains an oxygen contentfrom 0.01% to 20% by weight.
 7. The 3D humic acid-carbon hybrid foam ofclaim 1, wherein said foam has a specific surface area from 200 to 3,000m²/g or a density from 0.1 to 1.2 g/cm³.
 8. The 3D humic acid-carbonhybrid foam of claim 1, which is in a continuous-length roll sheet formhaving a thickness from 100 nm to 10 cm and a length of at least 2meters and is produced by a roll-to-roll process.
 9. The 3D humicacid-carbon hybrid foam of claim 1, wherein said foam has an oxygencontent or non-carbon content less than 1% by weight, and said porewalls have stacked hexagonal carbon planes having an inter-planarspacing from 0.3354 nm to 0.35 nm, a thermal conductivity of at least250 W/mK per unit of specific gravity, and/or an electrical conductivityno less than 2,500 S/cm per unit of specific gravity.
 10. The 3D humicacid-carbon hybrid foam of claim 1, wherein said foam has an oxygencontent or non-carbon content less than 0.01% by weight and said porewalls contain stacked hexagonal carbon planes having an inter-planarspacing from 0.3354 nm to 0.34 nm, a thermal conductivity of at least300 W/mK per unit of specific gravity, and/or an electrical conductivityno less than 3,000 S/cm per unit of specific gravity.
 11. The 3D humicacid-carbon hybrid foam of claim 1, wherein said foam has an oxygencontent or non-carbon content no greater than 0.01% by weight and saidpore walls contain stacked hexagonal carbon planes having aninter-planar spacing from 0.3354 nm to 0.336 nm, a thermal conductivityof at least 350 W/mK per unit of specific gravity, and/or an electricalconductivity no less than 3,500 S/cm per unit of specific gravity. 12.The 3D humic acid-carbon hybrid foam of claim 1, wherein said foam haspore walls containing stacked hexagonal carbon planes having aninter-planar spacing from 0.3354 nm to 0.336 nm, a thermal conductivitygreater than 400 W/mK per unit of specific gravity, and/or an electricalconductivity greater than 4,000 S/cm per unit of specific gravity. 13.The 3D humic acid-carbon hybrid foam of claim 1, wherein the pore wallscontain stacked hexagonal carbon planes having an inter-planar spacingfrom 0.3354 nm to 0.337 nm and a mosaic spread value from 0.2 to 1.0.14. The 3D humic acid-carbon hybrid foam of claim 1, wherein said porewalls contain a 3D network of interconnected hexagonal carbon planes.15. The 3D humic acid-carbon hybrid foam of claim 1, wherein said foamcontains meso-scaled pores having a pore size from 2 nm to 50 nm.
 16. Anoil-removing or oil-separating device containing the 3D humicacid-carbon hybrid foam of claim 1 as an oil-absorbing element.
 17. Asolvent-removing or solvent-separating device containing the 3D humicacid-carbon hybrid foam of claim 1 as a solvent-absorbing orsolvent-separating element.
 18. A method to separate oil from water,said method comprising the steps of: a. providing an oil-absorbingelement comprising the integral 3D humic acid-carbon hybrid foam ofclaim 1; b. contacting an oil-water mixture with said element, whichabsorbs the oil from the mixture; c. retreating the element from themixture and extracting the oil from the element; and d. reusing theelement.
 19. A method to separate an organic solvent from asolvent-water mixture or from a multiple-solvent mixture, said methodcomprising the steps of: a. providing an organic solvent-absorbing orsolvent-separating element comprising the integral 3D humic acid-carbonhybrid foam of claim 1; b. bringing said element in contact with anorganic solvent-water mixture or a multiple-solvent mixture containing afirst solvent and at least a second solvent; c. allowing said element toabsorb the organic solvent from the mixture or separate said firstsolvent from said at least second solvent; d. retreating the elementfrom the mixture and extracting the organic solvent or first solventfrom the element; and e. reusing the element.
 20. A thermal managementdevice containing the 3D integral humic acid-carbon hybrid foam of claim1 as a heat spreading or heat dissipating element.
 21. The thermalmanagement device of claim 20, which contains a device selected from aheat exchanger, heat sink, heat pipe, high-conductivity insert,conductive plate between a heat sink and a heat source, heat-spreadingcomponent, heat-dissipating component, thermal interface medium, orthermoelectric or Peltier cooling device.